A. Field of the Invention
The present invention relates to a damper mechanism and a flywheel assembly.
B. Description of the Background Art
In automotive vehicles, a damper mechanism is often included in a flywheel/clutch mechanism attached to the crankshaft of the automobile's engine, between the engine and a transmission for absorbing a torque variation produced by the engine. The damper mechanism may be disposed in either a clutch disk assembly or a flywheel of the flywheel clutch mechanism. The damper mechanism includes input and output members which can rotate relatively to each other, and also includes elastic members such as coil springs for restricting relative rotation of these members, and a friction generating mechanism which generates a friction to damp vibration when these members rotate relatively to each other.
For example, parts of a damper mechanism arranged between first and second flywheels of a flywheel assembly are disposed in a chamber filled with viscous fluid. Owing to lubrication by the viscous fluid, it reduces a friction between an elastic member and a support member and between other sliding portions at the friction generating mechanism or the like.
In the conventional damper mechanism described above, a film of the viscous fluid must be present between sliding portions of the elastic member and the support member, otherwise, wearing or abrasion occurs between the engaging sliding surfaces. When such a device sits unused for an extended period of time, gravity might cause such a film of viscous fluid to drain from some surfaces. Further, the viscous fluid may leak from the chamber, in which case a lubricity is further impaired.
In the damper mechanism, coil springs forming the damper mechanism require a circumferentially and axially large space due to their constructions. Therefore, it is difficult to arrange the damper mechanism of the above structure in a front wheel drive vehicle, in which an axial space is particularly restricted.
Japanese Laid-Open Patent Publication No. 6-174011 has disclosed a damper mechanism, in which an undulated or curved plate springs are used instead of coil springs for reducing a required space. Each undulated plate spring is formed of a plate member which has a constant width and a corrugated form. The undulated plate spring is formed of ring portions having open ends, and lever portions which connect the open ends of the ring portions for enabling a series operation of the ring portions. The paired lever portion extend in a diverging form from the common ring portion, and have a higher rigidity than the ring portion.
The undulated plate spring is arranged in an arc-shaped chamber defined by input and output members for transmitting a torque from the input member to the output member. When a torsional vibration is transmitted to the input member, the undulated plate spring is compressed in the rotation direction. Thereby, an open angle between the paired lever portions decreases, so that a bending moment is exerted on the ring portion. As a result, the ring portion and the lever portion elastically bend in the same direction around a fulcrum formed of a center (apex) of the ring. When the torsion angle increases, ends of each ring portion are brought into contact, and thereafter, the ring portion elastically bends around the fulcrum formed of the ends. An elastic energy is distributed and stored in the plurality of ring portions.
The lever portion has a higher rigidity than the ring portion, and has a uniform thickness. Therefore, the lever portion cannot store a sufficiently large elastic energy. As a torque transmitted to the damper mechanism increases, a relative torsion angle between the input and output members increases, so that the undulated plate spring is compressed to a larger extent. When a load larger than an ordinary torque is exerted on the undulated plate spring, an excessively large stress breaking the undulated plate spring may be produced at the bent plate spring.